You will see a list of the apps after a minute or so, with the apps taking up the most room at the top of the list.

Some general advice:

Photos

Assuming you have setup Google Drive correctly to automatically upload your photos and videos, you’ll still have a copy of them in Drive, even if you delete them from your iPad. [They’ll be the Google Photos folder on Drive].

To ACTUALLY delete photos/videos from your iPad, open up Photos –> Camera Roll.
Click SELECT.
Click on the photos/videos you want to delete.
Click the Trash icon, top left.
Click the message “Delete these x photos?”
Click “Albums”, top left
Open up “Recently Deleted”
Click “Select”, top right
Click “Delete All”, top left.

If you don’t clear out the Recently Deleted folder manually, it will empty itself in about a month.

Google Apps [Drive / Sheets / Docs]

The Google apps all have an option to store your document “locally” on the iPad. If you no longer need docs available when you don’t have an internet connection, then check the Docs part of this article: iPads –> what’s taking up all my storage?

Miscellaneous Space Hogs

Messages – those messages with pictures and videos take up ROOM. Delete them.

Mail – sometimes the Mail app takes up a ton of room. Actually, it’s all those emails that you never deleted. Delete them.
–> If deleting the mails sound like too much, then delete the account
[Settings –>Mail–> Accounts–>Select the account–>”Delete Account”
–> This does NOT actually delete your account from the Mail server – it just deletes your “window” into your mail account.
–> Then re-create it. For the MDS email, it’s a Google account type.

iMovie – delete your projects. You can export them into your Google drive if you’d like a copy of your final project.

Notability – anything deleted in Notability goes into a trash can which is emptied after about a month [similar to the way Photos works]. Click on the trash can to empty it manually.
Remember that deleting a note in Notability does NOT delete it from Drive.